American chapter of the multiplane saga is surprisingly "meaty". During the Great War, Curtiss Aeroplane and Motor Company designed numerous triplanes.
Here is an artist's impression of the Curtiss Triplane flying boat, published in the Flight magazine (UK) in 1916. The real thing was even more impressive. In 1915, the American businessman Rodman Wanamaker commissioned Curtiss to build a new, larger flying boat, which became known as the Wanamaker Triplane, or Curtiss Model T in Curtiss's then-current designation scheme (It was later retroactively re-designated Model 3 when Curtiss changed its designation system).
Early press reports showed a large triplane, 68 ft (17.9 metre) and with equal-span six-bay wings of 133 foot (40.5 metre) span. The aircraft, to be capable of carrying heavy armament, was estimated all-up weight of 21,450 pounds (9,750 kilogrammes) and was to be powered by six 140 hp 104 kW) engines driving three propellers, two of which were to be of tractor configuration and the third a pusher.
The British Royal Naval Air Service (RNAS) placed an order for 20 of the new triplanes with the first one being completed at Curtiss's factory at Buffalo, New York in 1916, the first four-engined aircraft to be built in the United States and one of the largest aircraft in the world. While of similar size and weight to the aircraft discussed in the press, the Model T had uneven span wings, with the upper wing having a span of 134 feet, while it was planned to be powered by four tractor 250 hp (187 kW) Curtiss V-4 engines installed, unusually for the time, individually on the middle wing. The two pilots and flight engineer were provided with an enclosed cabin, similar to that in the Curtiss America, while to reduce control loads, small windmills could be connected to the aileron cables by electrically operated clutches to act a form of power assisted controls.
The planned Curtiss V-4 engines were not available when the prototype was completed, so it was not flown in the United States, but was taken to England by ship and re-assembled at the Seaplane Experimental Station at Felixstowe, being fitted with four French 240 hp (180 kW) Renault engines. Although later re-fitted with four 250 hp Rolls-Royce Eagles, it was unsuccessful, with the order for the remaining twenty being cancelled.
Just like the Model T, smaller Curtiss military triplanes never saw combat.
The Curtiss Model L was a triplane produced as a trainer aircraft in the United States in 1916. A largely conventional design with the upper two wings of equal span and a shorter-span lower wing, the Model L had a wide open cockpit that accommodated the student and instructor side-by-side, an unusual feature for its time and which gained the aircraft the nickname of "Sociable Triplane".
In 1917 the United States Navy ordered five scout aircraft from Curtiss, they were designated the GS for Gnome Scout, named for the French-built 100 hp (75 kW) Gnome rotary engine used to power the aircraft. The GS was a biplane with a central float and a stabiliser float at each end of the lower wing. The Navy ordered an additional aircraft as a triplane, which was designated the GS-1 and the original aircraft was retrospectively designated the GS-2.
Although they were delivered to the Navy in 1918 nothing further is known about the type, other than that the GS-1 was destroyed in a landing accident on 1 April 1918.
The Model S was Curtiss' first attempt at a fast and maneuverable single-seat fighter. The first variant, S-1, had disappointing performance. In March 1917, new wings were attached to the S-1 fuselage and the project was redesignated S-2. In 1917, the S-3 became the first triplane in service in the United States.
Color profile of the Curtiss S-3 by W.I. Boucher @ wwiaviation.com
In 1918 and 1919, Curtiss experimented with seaplane versions of the S-3, designated S-4 and S-5. The S-6 was intended to be an improved S-3, but performance was poor and of the 12 ordered by the USASC, only 1 was delivered.
The Curtiss 18T was intended to protect bombing squads along the French coast, and a primary requisite for this job was speed. Speed was not the triplane's only salient feature: an 18T-2 set a new altitude record in 1919 of 34,910 ft (10,640 m). The streamlined and very "clean" fuselage contribiuted to the aircraft's performance. The basic construction was based on cross-laminated strips of wood veneer formed on a mold and attached to the inner structure. The technique was a refinement of that used on the big Curtiss flying boats.
The Model 18T-2 was an improved version of its predecessor, boosting 50 additional horsepower. The wings of the new model were swept back. It was also 5 ft (150 cm) longer with a 9 ft (270 cm) longer two-bay wing, though its flight ceiling was 2,000 ft (610 m) lower.
Color profile of the Curtiss 18T by W.I. Boucher @ wwiaviation.com
After World War I, it was employed as a racing plane: an 18T-2 nearly won the Curtiss Marine Trophy Race in 1922 (limited to U.S. Navy pilots), but pilot Sandy Sanderson ran out of fuel just before the finish line.
And, for a dessert, more Curtiss triplanes: